The present invention relates to an image display apparatus and, more particularly, to a head- or face-mounted image display apparatus which is retained on a user's head or face to project an image into an observer's eyeball.
In recent years, helmet- and goggle-type head- or face-mounted image display apparatuses have been developed for virtual reality or for the purpose of enabling the user to enjoy a wide-screen image personally.
For example, Japanese Patent Application Laid-Open (KOKAI) No. 2-297516 discloses an image display apparatus including, as shown in FIG. 16, a two-dimensional display device 1 for displaying an image, an objective collimator lens 2, and a parallel transparent plate 3 having off-axis parabolic mirrors at both ends thereof. Image display light from the two-dimensional display device 1 is formed into parallel rays through the objective collimator lens 2. Thereafter, the light rays successively undergo a first transmission by one of the parallel surfaces of the parallel transparent plate 3, a reflection by the first parabolic mirror, some total reflections in the parallel transparent plate 3, a reflection by the second parabolic mirror and a second transmission by the other of the parallel surfaces (a total of 8 reflections and a total of 2 transmissions), thereby forming an intermediate image at the point F and projecting the intermediate image into an observer's eyeball 4.
U.S. Pat. No. 4,026,641 discloses an image display apparatus in which, as shown in FIG. 17, an image displayed by an image display device 1 is converted into a curved object image by a transfer optical element 5, and the object image is projected into an observer's eyeball 4 by a toric reflecting surface 6.
In an image display apparatus of the type in which an image of an image display device is relayed, as shown in FIG. 16, a relay optical system is needed in addition to an ocular optical system. Consequently, the entire optical system increases in both size and weight, and an amount by which the optical system projects from the observer's face or head also increases. Therefore, this type of image display apparatus is not suitable for use as a head- or face-mounted image display apparatus.
In the optical system that focuses parallel rays to form an intermediate image, and also in the optical system that projects an intermediate image into an observer's eyeball, only the parabolic mirror has power. Therefore, exceedingly large aberrations are produced in these optical systems.
When a concave mirror alone is used as an ocular optical system as shown in FIG. 17, even if the concave mirror is a toric surface as in the case of FIG. 17, the ocular optical system produces exceedingly large aberrations, causing the image quality to be degraded.
Accordingly, it is necessary to use a transfer optical element 5 such as a fiber plate for correcting field curvature produced by the ocular optical system. However, comatic and other aberrations cannot satisfactorily be corrected even if the transfer optical element 5 and the toric reflecting surface 6 are used.